The Ebola Virus: Virology, Fiction and Threat to Mankind, F.A. Murphy

DR. FREDERICK A. MURPHY TALKS ABOUT THE EBOLA VIRUS

An Interview by Sean Henahan, Access Excellence

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The book "The Hot Zone" and the film "Outbreak" have seized the public's imagination and brought into focus many issues regarding the very real threats posed by new and emerging diseases. In this interview we talk with Frederick A. Murphy, D.V.M., Ph.D., Dean of School of Veterinary Medicine, UC Davis.

At the time of the 'Reston incident', Dr. Murphy was the director of the National Center for Infectious Diseases at the CDC in Atlanta. Dr. Murphy is considered one of the world authorities on viruses. He was the first one to look at Ebola virus 'face-to-face' in the electron microscope. Dr. Murphy appears in "The Hot Zone" and his now famous photo of the Ebola virus appears in the film "Outbreak".

Note: Dr. Murphy has also provided an extensive [1]bibliography and[2] three excellent electron micrographs to accompany this interview.

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Q: The book "The Hot Zone" and more recently the film "Outbreak" have brought public attention to the reality of emerging viruses and potentially disastrous epidemics. It can be difficult to tell fact from fiction with these kind of sources. I'd like to ask some questions gathered from high school science teachers and students all over the country to clarify some of the issues raised by this book and this movie.

A: The public response to the book and the film has been phenomenal. Half of the posts for a [3]virology conference on the Internet I look at are about the Ebola virus. I myself have had innumerable calls from the press and other media people. By the way, I want to say hello to the Access Excellence people and say I had a great time down at Genentech last summer when I spoke on the subject of new and emerging diseases.

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Q: Please explain how Ebola and the other filoviruses are classified and how they are related to other known viruses?

A: The viruses are classified in the family 'Filoviridae', with one genus, 'Filovirus'. There are four known viruses. We have Marburg virus and three Ebola viruses: Zaire, Sudan and Reston. Marburg and Ebola are distinguished by their length when purified. In the unpurified state you get all different lengths of these worm-like virions. When they are purified, the infectivity is associated with a particular particle length, which is slightly different between the Marburg and Ebola, but all of the Ebola viruses are the same length.

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Q: Considering how similar the Ebola viruses are, how are they differentiated?

A: They are very close. First of all, there is a very small serologic difference among the Ebola viruses which can help distinguish them. Second, there are sequence differences which can be determined using the tools of molecular biology.

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Q: What have we learned about the Ebola genome, and what remains to be learned?

A: Ebola Zaire has been completely sequenced and Ebola Reston is nearly completed. The gene order of these viruses reaffirms their independence as a family. Also, some ancient conserved sequences along with the gene order, i.e. the layout of the genes along the RNA molecule, put the family 'Filoviridae' into an order, the only order in virology, 'Mononegavirales' This emphasizes the ancient phylogenetic connection between three families- 'Filoviridae', 'Paramyxoviridae' (measles, mumps) and 'Rhabdoviridae' (rabies). There is no connection with HIV.

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Q: Let's talk about the pathogenicity of Ebola. How does Ebola virus infect humans?

A: In Zaire and Sudan, Ebola virus was spread by close contact and dirty needles. The center of the epidemic in Zaire involved a missionary hospital where needles and syringes were re-used without sterilization. Most of the staff of that hospital got sick and died. There were secondary cases involving people taking care of sick people or preparing bodies for burial, but the virus essentially shut down after that epidemic peaked.

There is something of a misconception that Ebola virus can infect just about any cell. In fact, the virus has a very specific tropism for liver cells and cells of the reticuloendothelial system, e.g. macrophages. Massive destruction of the liver is a hallmark feature of Ebola Zaire, Ebola Sudan, and Ebola Reston (the latter in monkeys only).

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Q: Ebola Zaire is said to kill nine of ten people infected. What about the surviving one person? Is anything known about natural resistance to this virus?

A: Starting with Marburg in 1967, there was one fellow who tested positive for the virus 30 days post-infection. In fact the virus was detected in his semen, and there was a case of sexual transmission in that circumstance. Another patient had virus in the vitreous of his eye for more than 30 days. But eventually the virus died out within these people without killing them. Ebola too is not persistently carried in the blood and appears to be self limiting in the surviving patient.

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Q: Given that there are some signs of natural immunity to Marburg and Ebola Zaire, and that the monkey workers were not killed after exposure to Ebola Reston, does this give us any possible approaches to vaccine development? Both the measles and rubella vaccines were based on attenuated viruses.

A: No, I don't think so. I don't think we would know how to select a stable, safe attenuated virus. The kind of research needed to develop a modified live virus vaccine simply could not be done given the scope of the problem. That is, you only have a few people working in labs who would need to be vaccinated, and you might want a vaccine stockpile in the event of an epidemic, but these are not the scale of circumstances where we could afford to develop a vaccine. A killed vaccine is much simpler to develop, but so far this has not worked with Ebola virus.

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Q: On Oct 13, 1976 you prepared a specimen from an African patient with hemorrhagic fever and suddenly realized it might be deadly serious. Can you tell us what you were thinking at that time?

A: When I put the specimen in the electron microscope, I was sure it was Marburg. I had worked on Marburg in 1967 and 1968 and had done a project on experimental Marburg infection in monkeys. The specimen had come back from Zaire to the CDC in Atlanta in less than optimal condition, with the tubes in the box broken. Anyone else would have taken a look and put the whole box in the autoclave, but Dr. Patricia Webb, wearing gloves, gown and mask, squeezed a few drops of fluid out of the cotton surrounding the broken tubes. That was the material the virus was isolated from. It was placed in tissue culture (monkey kidney cells) for a couple of days then I got a drop of the tissue culture fluid and prepared a specimen for the electron microscope. When I saw what I was sure was Marburg, I shut the electron microscope down and went back to the room in which I had prepared the specimen. This was in the days when hoods were a lot more primitive. I "cloroxed the hell" out of the place where I had done the preparation and carried my discard pan with gown and gloves etc. to the autoclave and ran it. Then I went back to the microscope and called Karl Johnson and Patricia Webb to take a look. I shot a cassette of pictures and with wet negatives, not good for the enlarger and I made prints which were available within minutes. I carried these dripping prints to the office of the Director of the CDC. It was very dramatic.

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Q: Then later when Fort Detrick called and said they thought they had found Ebola in Virginia, what was your reaction?

A: The way it is stated in "The Hot Zone", General Russell suggested I didn't believe him. In fact, I took it very seriously. General Russell himself had enough experience to recognize Ebola when he saw it. With Marburg 67, it was monkeys that brought the virus to Europe. In 1976 we had no idea where the virus came from, so when he said he had Ebola in monkeys I sure believed him. We went to Fort Detrick the next day.

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Q: There are a number of issues concerning the response to an epidemic raised by both "The Hot Zone" and "Outbreak". How well did these describe the interaction of the various agencies?

A: The movie Outbreak created some false impressions. The law in our country gives the responsibility for epidemic management to state health departments, with these agencies calling the CDC when they need help. CDC has no authority to go into a state except by invitation. The Army could be called in by a state health department, but to my knowledge this never has happened.

In the Reston incident, the Virginia Health department and the CDC took over the human health side of the episode and the Army, at the request of the monkey import company, took over the animal side. It turned out after lots of surveillance of animal caretakers and their families that there was no human disease, but there was plenty of monkey disease. The Army's role involved depopulating the monkey colony. So the movie Outbreak, where the Army takes over, is rather fictional.

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Q: Has the Reston incident changed the way monkeys are imported and housed?

A: There were a series of CDC investigations after the Reston episode. There was also a complete embargo on the importation of monkeys for about a year. The CDC then relicensed importers, denying licenses to those that did not have proper facilities and staff training. So I would say there has been significant improvement in this area. Countries that used to export monkeys are also getting out of that business. primarily for species preservation reasons.

The use of captive bred monkeys is absolutely the trend. The goal is for complete reliance on domestic breeding. We have to stretch the definition a bit, since there is a huge captive breeding colony on a small Caribbean island.

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Q: Did anyone every figure out how an African Ebola virus ended up in a monkey from the Philippines?

A: No. That's a very good question. We still have no idea where Ebola lives in nature. It was not possible to do field studies in the Philippines because of a civil war going on in the area the monkeys came from. Some studies in Africa tried to trace Marburg and Ebola, but nothing has ever been found.

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Q: Are budget cuts affecting the ability of the CDC and other agencies to respond to epidemic outbreaks?

A: Yes. The Army program at USAMRID has been cut quite a bit. Over the past few years the CDC's programs for dealing with infectious diseases have been nibbled to death by inflation. The budgets are the same in today's dollars as they were 12 years ago. In effect these programs have lost half of their purchasing power, while at the same we've seen an explosion in AIDS and other infectious diseases.

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Q: Such as Hantavirus?

A: Yes, hantavirus is a good example. The same people from CDC and the Army who worked on the new Hantavirus outbreak previously worked on Ebola. It is a small, wonderful group of dedicated people. They really have had their budgets whacked. And then with the emergence of one disease problem after another, this has really stretched them beyond the breaking point.

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Q: Can you give us an update on the Hantavirus situation?

A: It is amazing how quickly the virus was characterized after the first outbreak in the Four Corners area. The virus is transmitted by breathing dried dust that contains the virus (from the dried feces, urine and saliva of the mouse vector, 'Peromyscus maniculatus'). The virus could not be grown, so everything was done by molecular biological means. The first clue came with the observation of some cross serology with known hantaviruses. Everything else was done by PCR and partial sequencing. Six months later they were able to make an isolate. Since then four different variants of the virus have been isolated from more than 100 people. It still has a mortality rate above 50% and has been seen from California to the East Coast and Florida. It is incredible that this set of variant viruses was present all along and no one knew it. Although we know the vector, we also know that controlling this vector, mice, is virtually impossible.

We have a similar problem now in California, with all the rains. The mosquitoes that carry Western equine encephalitis and St. Louis encephalitis are resistant to virtually every licensed insecticide. We could have a re-emergence of these virus diseases this summer.

The most important mosquito-born disease in the world today is dengue. This disease is emerging now in all the big cities of the Caribbean and tropical and sub-tropical America. If you get lots of dengue and multiple serotypes in an area, you get dengue hemorrhagic fever. Uncomplicated dengue infection, called breakbone fever, is like influenza, with all people recovering. But dengue hemorrhagic fever, usually seen in children, is deadly. Symptoms include fever, shock, hemorrhaging from the nose and mouth, respiratory distress and, in some cases, death.

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Q: Back to the CDC. What do public health agencies need in order to fight epidemics?

A: The things they need are hard to come by. The National Academy of Sciences, the Institute of Medicine and the CDC have [4]published plans on what is needed to control new and emerging diseases better. The plans focuses on better surveillance, better laboratory diagnostics, better communication and better education. The plans are very good, but the timing is terrible, since budgets are so tight, and from what I read in the papers, budgets will get much worse.

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Q: There have been complaints at the vast inaccuracies and dubious details in the film Outbreak. What did you think of this film?

A: I did see the movie. In fact, in return for the use of the electron micrographs of the virus, Warner Bros. gave us tickets to the premiere in Sacramento. I thought the early scenes in the biosafety level 1,2,3, and 4 labs looked pretty accurate. After that it became fictional, and I enjoyed it as fiction. We know a virus can't kill someone in an hour. The making of the antisera in a day was ludicrous. I think all bug movies have a problem, since once they unleash the bug, there is the problem of resolving the crisis. Like in the film, 'The Andromeda Strain', the only way to resolve the story was to have the bug mutate to become harmless. The real world is not so simple. Fourteen years into the AIDS epidemic and we still don't have a vaccine or decent drugs.

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Q: The CDC is one of two places in the world with remaining specimens of smallpox virus. Both the CDC specimens and the Russian specimens were scheduled for destruction, but have gained a reprieve. Should they be saved?

A: The collections of smallpox specimens at these places are fairly large. CDC has about 500 strains of the virus. It is highly contained in a freezer that is never opened. The WHO also visited the Russian facility and certified its safety.

I was originally in favor of the destruction of these specimens. This was for political reasons, rather than scientific ones. I thought the publicity surrounding its destruction would remind people that we had done something very good. However, within the last two years several different strains of the smallpox virus have been completely sequenced. Some really interesting genes have been found, which may contribute to the understanding of the pathogenicity and natural history of other viruses. So the current consensus is that these kinds of genes must be preserved and studied.

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Q: Last question. Any advice for some one considering a career in virology?

A: There are several kinds of virologists. One kind of virologist is a molecular biologist who studies the nature of the virus and how it works. That is the world of molecular biology and cell biology. Virology is also an infectious disease science in the hands of physicians and veterinarians who take specialty training. Virology also interfaces with other areas of biology that have to do with how viruses are transmitted, such as entomology and mammology. The field of virology also includes the whole world of public health and preventive medicine.

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